Navigation and guidance control for automated guidance vehicles are described in GB-A-2,158,965 and U.S. Pat. Nos. 4,847,769, 4,816,998 and 5,175,415. GB-A-2,158,965 and U.S. Pat. No. 4,847,769 both describe vehicles in which the movement is predicted by a dead reckoning system which determines the position of the vehicle at any given time by sensing the steering angle and the angle of rotation of a controlled steering caster during a short time interval. U.S. Pat. No. 4,847,769 further describes a system where the predicted position is frequently checked and corrected against an actual position determined by a vehicle mounted laser scanning and reference frame mounted target system. The error between the predicted position and the actual position is utilized to determine an average crabbing angle which is fed through a Kalman filter calculation and used as a correction factor in calculating the next predicted position of the vehicle.
U.S. Pat. No. 4,816,998 discusses a vehicle that uses a caster wheel having both an angle measuring sensor and a wheel rotation measuring sensor for enabling the navigation and guidance system to calculate a mean distance traveled, a change in angle of an axis on the vehicle and vehicle heading change assuming ideal travel along a fixed radius arcuate path.
U.S. Pat. No. 5,175,415 discusses an apparatus for measuring the forward and reverse movement of a vehicle by placing a separate encoder wheel adjacent to each non-pivoting drive wheel.
All of the navigation and guidance systems heretofore are limited because none of these systems determine their current position by measuring and accounting for the lateral movement of the vehicle. The lateral movement of the vehicle is often referred to as crabbing, scrubbing or side slip. The lateral movement of the vehicle is determined with respect to the vehicle's pivot point. This is typically a location along the longitudinal centerline of the vehicle that the navigation and guidance system attempts to direct along the selected path. A vehicle may experience lateral motion for a variety of reasons, for instance, when the vehicle is: i) misaligned, ii) turned, where the wheels pivot, distort and/or slip, and iii) intentionally steered laterally. Accordingly, the overall tracking accuracy of the systems heretofore is compromised by their inability to measure and account for the lateral movement component in the vehicle's change of position.
It is therefore an object of the present invention to provide a vehicle with a system that determines the change of position of the vehicle regardless of the direction the vehicle travels.
It is another object of the present invention to provide a vehicle with a system that can measure and determine the movement of the vehicle in the forward, reverse and any lateral direction.
It is yet another object of the present invention to provide a vehicle with a navigation and guidance control system that adjusts the steering of the vehicle responsive to the lateral movement of the vehicle.
It is a further object of the present invention to provide a vehicle with a navigation and guidance system on-board the vehicle that steers the vehicle taking into account the vehicle's lateral movement, without requiring an absolute position referencing system that utilizes off-board position identifiers, reflectors or reference markers.
It is still another object of the present invention to provide a vehicle equipped with an angular motion sensor and a freely pivoting caster wheel having a free-wheeling track wheel for sensing the vehicle's movement in two-dimensions with respect to the vehicle frame reference.
It is still a further object of the present invention to provide a vehicle with a navigation and guidance system equipped with a gyroscope and a freely pivoting spring loaded caster wheel having a spherical shaped contact surface, that senses the change of position of the vehicle in two-dimensions, to provide better control of the vehicle.
It is yet a further object of the present invention to provide a vehicle with a navigation and guidance system equipped with a gyroscope and a distance travelled and vehicle rotation sensing caster that allows the caster to be mounted at any location on the vehicle.
It is still a further object of the present invention to provide a vehicle controlled by a navigation and guidance system equipped with an angular motion sensor and a free wheeling, freely pivoting, non-load bearing track wheel caster that detects movement of the vehicle in two-dimensions, with respect to the vehicle frame reference, to provide more accurate control of the vehicle.
These and other objects of the present invention will become readily apparent after studying and understanding the present invention, as hereinafter described.